I have tried and still use some of the various devices (Gingko, maple wood block, Symposium, Black Diamond cones etc...) they do make an audible difference but not major in my case, just more fine tuning to taste I guess. Whether they were making up for some negative somewhere else in the system or not, but I heard differences. If I was using a purpose made rack or stands then I would be less likely to use such devices. I have mostly moved to various forms of wood, granite and cork and use the other devices less now.
I have especially noticed differences under any component that has moving parts.
Now if I had issues with my system I would obviously look at room treatments and electrical delivery before using other tweaks as that's where my biggest non-component gains have come from.
Now given that one can likely find some granite for cheap or free, If just starting in this area, I'd happily go that route with granite and some of those cork/rubber footers and call it a day. Everyday, I drive by a graveyard (creepy I know) and they have slaps of 5 inch+ granite that the groundskeeper was going to give me for free but I don't need it.
Builder sites, local Habitat for Humanity, salvage yards etc... usually have granite remnants there as well, I can get granite easy in my area. I've got chunks lying around that I collected. Also concrete pavers from Home Depot may work if it fits your system, maybe not SOTA for the audiophile but if you want cheap and effective isolation, maybe not vibration draining or tuned isolation but good isolation none the less. If I needed something under a big amp. or speakers I would go this route first, concrete atop inexpensive spikes or cork/rubber pads. If you can find some 1/2 inch thick or more acrylic that's good too.
Try a big concrete paver (you can spray paint it or cover it in a fabric with spray adhesive) below (and atop) your subwoofer (mass loading I guess) made a nice difference to my ears. Also Plasi-clay or mortite on components with moving/spinning parts works well too. The better your system is put together, the less likley these devices will make substantial improvements IMO, unless we are talking about specific tuned devices in the more expensive isolation/vibration products. In many cases I think these devices may be just lowering or changing the resonant freq. and that's the audible difference I heard and that may be achieved more economically with accessible off the shelf products, but I'm not even close to well educated on these matters, just my opinion.
